Screw



Patented June 8, 1937 UNITED `s'rirras PATENT OFFICE 2,083,092 sca'Ew :mph n. mener. Detroit. Mien.

Application January 20, 1936, Serial No. 59,866

'1,Claims.

mation of the cap and the socket which is formed therein. Y

Heretofore it was customaryto form the sockets of cap screws with a square, hexagonal or a splined-circle cross contour. I have discovered,`

however, that certain marked improvements in.

the strength of the screw, its methodl of manufacture and its ease of operation could be obtained were the socket formed or designed on a diilerent principle.

It is another object of my invention to provide an improved screw, thesocket cross contour of which consists of a series of alternating concave and convex arcs tangentially joining each other so as to form a plurality of equispaced inections.

Another object is to provide such a screw socket with'inections having an angle of incidence or pressure relative to the radial line drawn from the center of the screw not to exceed about 40.

Another object is to provide a socket headed 25 screw of new and improved construction which is economical to manuiacture both with respect to material and labor, and yet has a head capable of withstanding forceful tightening without spread ing.

These and other objects will become more readily apparent from the following detailed descrip-f tion takenin connection with the accompanying drawing, in which:

Fig. 1 is a plan view of a preferred form of the 35 invention embodied in a cap screw.

Fig. 2 is an elevation thereof, the cap of the screw being shown in cross section.

Fig. 3 illustrates a handwrench (on a reduced scale) which is suitable for rotating the screw 40 shown in Figs. 1 and 2.

Fig. 4 is an enlarged cross section of the wrench.

Fig. 5 is a diagrammatic view (enlarged) showing the contours of the socket and the wrench when in operative engagement.

45 I Fig. 6 is a geometricalv diagram showing the relation between the normal, tangential and spreading forces involved.

While I have illustrated in thel drawing an shall herein describe a preferred form of the in- 50 vention, it is to be understood that I do not intend to limit the invention to the particular arrangement shown, it being contemplated that those skilled in the art may devise various modiiications and alternative constructions without departing 55 from the spirit and scope of the appended claims.

In the iorm selected for purposes of disclosure,

the improved screw consists of a head or cap II A (Figs. 1 and 2) integral with a shank-I2 upon which the screw thread lI3 is cut or (preferably) rolled. The outside diameter of the screw thread I3 is the same a-s that oi the bolt I2 while the diameter of the cap II is about iifty per cent greater. A socket I4 is formed in the cap so as'to provide a prismatic cavity or indentation concenf tric with the cap I I and with a depth about onehalf of the height of the cap which height again is about the same as the diameter o1 the bolt I2. The cross sectional contour of the socket III is composed of a plurality (usually eight, but preferably seven or more) semicircular protuberances I5 and similar cavities I6 respectively adjoining each other in equispaced and comparatively short straight lines of inection Il.

As shown in the drawing,the centers of the protuberances I5 are all situated in a circle I8 coinciding with the bottoms of the cavities while those of the cavities are all in a circle I9 coinciding with the tops of the protuberances, from which it follows that the radii 20 forming the protuberances and the cavities are alike and equal vto the distance between the circles I8 and I9. In

proportioning this socket I have found from calculations and experiments that a markedly improved screw results when the diameter of the outer circle I8 is about seventy per cent of the cap diameter, and the radii 20 areA about seven per cent of the said cap diameter. Under these conditions any two infiectional tangent-s I'I adjacent to any cavity I6 will form an included angle A of about 45 and a pressure angle B of about 34 15'. The importance of this proportioning will be explained hereinafter.

In Figs. 3 and 4, there is shown a wrench 2l adapted to be used for actuating the screw I2 when the end 2|' is inserted in the socket I4A (Fig. l), the end 2i serving as a handle. The wrench is of conventional length and shape and the only point of interest lies` in the formation of its cross contour (Figs. 4 and 5). This contour also consists of alternate protuberances and cavities, the radii 23 of the protuberances and the radii 23 of the cavities respectively being the same as the radii 20 in Fig. 1, while diameters of the outer circle 24 and the inner circle 25 of centers of the radii are from ve to ten-thousandtlis oi' an inch less than the corresponding diameters I3 and I9 (Fig. 1). .By this means I prevent the wrench from engaging the socket I4 at tops and bottoms of the teeth, the contact (1) N=T c B The radial force -S tending to spread the socket outwardly is represented by (2) S= T tan B If I denote now the total torque acting upon the screw with the letter Q and the radius OD with r, I have Q 2o (3) n :El

where n is the number of teeth in engagement. Looking now at the Equations (1), (2) and (3), it follows that lt is advantageous to have, first, 25 a great number of teeth n, second, the teeth should be on a large radius r, and, third, the teeth should have a small pressure angle B. By reducing the pressure angle B, both the radial (S) and normal (N) forces are reduced from which it follows that the thickness of wall around the socket, the depth of the socket and the surface required to carry the normal force (N) are all reduced. A limit, however, is reached from the fact that ,the protuberances must be wide 35 enough to carry the shearing force T, and the iniiectional tangents must possess suillcien't taper to accommodate the wrench within practical workmanship limits.

The advantages .of my invention are rst that o the grooves are comparatively shallow, of liberal radii of curvature and free from sharp corners, second, the force distribution is favorable thus enabling the use of a comparatively -shallow socket, and third, the wrench projections are well 45 rounded thus protecting the workers hands. I have found it entirely practical to form such sockets by means of protrusion (upsetting) which could not be done if the socket possessed sharp or nearly sharp corners or if it were too deep. 50 By forming the thread on the shank of the screw by means of a cold rolling operation, and forming the socket by means of an upsetting operation, the entire screw may be nished without the use of any expensive machine operations, thus providing a screw which is extremely economical to manufacture and which embodies great strength.

I claim as my invention:

1. A screw comprising la head having a socket the cross contour of which consists of a series of alternating concave and convex arcs equally spaced and tangentially joining each other all about the circle.

2. Al screw comprising a socket having a peripheral wall consisting oi' a plurality of semicylindrical protuberances equally spaced about the socket.

3. In a screw a socket havinga cross contour consisting of a plurality of semicircular protuberances alternating with an equal number of semicircular cavities equally spaced about a circle concentric with the axis of the screw.

4. In a screw, a head having a socket the peripheral wall of which consists of a plurality of alternating semicylindrical projections and depressions so arranged that the adjacent projecjections and depressions tangentially merge one into the other at an angle not exceeding 45 as measured from the radial line drawn from the axis of the screw to the point of inflection.

5. A screw comprising a socket having a cross contour of the form of an undulating wave line forming alternate projections and depressions of substantially the same radii of curvature and a plurality of equispaced inilectional tangential straight lines interposed between and joining the said projections and depressions and constituting thebearing surfaces for the wrench.

6. A screw having a head formed with-a sha1- low socket provided with a peripheral wall comprising alternate semicylindrical projections and depressions.

7. The combination of a socket head screw and a wrench for turning the same in which the socket cross contour consists of a plurality of teeth and spaces of a semicircular shape all possessing the same radii of curvature and the cross contour oi' the wrench consists of teeth and spaces of the. same radii oi curvature as the socket, but distributed along the circumference of a smaller circle.

JOSEPH R. RICHER. 

